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Old 09-10-2008, 02:50 PM
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Charging system 911

I just bought 2 new motor-craft batteries on Friday, truck has been running great. This A.M. I go out and notice it is turning over a little slow. The next time it is completely dead.
I get a jump and on the way home I notice the battery gauge is down under the 8 ! So when I get home I take the negative battery cables off of both batteries and it dies!
Now on a gasser this most likely would mean that the alternator is bad, but I don't know about the 7.3 powerstroke. I do know there are some relays and things my book says to check.

Is there a "general" part that burns out or something easy to check for?
All help is greatly appreciated.
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Old 09-10-2008, 03:01 PM
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Either by using a volt meter or by taking it to an autoparts store test the out put of the alternator. The out put should be around 14 volts. If your alternator is putting out anything less then 13 volts. I would say it is bad and needs to be replaced.

You can test it with a volt meter by the big stud on the back of the alternator. With the truck running place the red lead on the stud and ground the black lead out. You should get a steady reading between 13.4-14 volts. Anything below 13.0 volts I would look at replacing the alternator.


Oh and the volt gauge on the dash is reading off the alternator.
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Old 09-10-2008, 03:01 PM
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Old 09-10-2008, 03:02 PM
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Quote:
Originally Posted by bigcountrysg View Post
Either by using a volt meter or by taking it to an autoparts store test the out put of the alternator. The out put should be around 14 volts. If your alternator is putting out anything less then 13 volts. I would say it is bad and needs to be replaced.

You can test it with a volt meter by the big stud on the back of the alternator. With the truck running place the red lead on the stud and ground the black lead out. You should get a steady reading between 13.4-14 volts. Anything below 13.0 volts I would look at replacing the alternator.
Thanks, I'll check it with a volt meter when the batteries are charged enough to start it.
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Old 09-10-2008, 03:02 PM
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Quote:
Originally Posted by sevenmalards View Post
you bump because you do not like my response.
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Old 09-10-2008, 03:38 PM
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Originally Posted by bigcountrysg View Post
you bump because you do not like my response.
Funny, we posted at the same time!
Here is a "dumb" question:
What setting do I put my volt meter on, A/C or D/C?
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Old 09-10-2008, 03:42 PM
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Set the meter to DC.
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Old 09-10-2008, 03:45 PM
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You put it on dc, you can check alternator ripple voltage with ac... but thats for a different day. I would not condemn an alternator just based on voltage. Ive seen them put out voltage, but not amperage... So itd be best to actually load test the alternator with a carbon pile. Then once ya figure out amperage and oltage you should make sure all the wiring for the alternator is ok first,like fuses, and current for the field windings.

Last edited by WEWILLE; 09-10-2008 at 03:48 PM.
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Old 09-10-2008, 08:14 PM
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Well I just got home from class and checked the alternator and got 10.5 volts. I couldn't even roll my windows up when I pulled in from class. New alternator tomorrow, and honestly with 250K on the ticker I was wondering when it was going to go.

Thanks everyone!
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